1. Field of the Invention
The present invention relates to a semiconductor photonic device, and more particularly to a semiconductor photonic device comprising group III-V compound semiconductor, such as GaN, InGaN, GaAlN, InGaAlN.
2. Description of the Related Art
As a material for forming a semiconductor photonic device such as light emitting diode (LED) or laser diode (LD) for generating lights from a blue light through an ultraviolet light, there has been known a group III-V compound semiconductor represented by a general formula In.sub.x Ga.sub.y Al.sub.z N (x+y+z=1, 0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1). Since such kind of compound semiconductor is a direct transition type, it has a high light emitting efficiency. Further, since it is possible to control the wave length of a light being emitted by controlling In concentration, said compound semiconductor has attracted public attention.
Since it is difficult to manufacture a large scale single crystal by using the In.sub.x Ga.sub.y Al.sub.z N when a film of such crystal is to be manufactured, a process called hetero-epitaxial growth is used to grow the crystal on substrates of different materials, in general, it is usual that the crystal is allowed to grow on a C surface sapphire substrate and a Si substrate.
However, since the C surface sapphire substrate and Si substrate do not have a matched lattice with the compound In.sub.x Ga.sub.y Al.sub.z, there is a problem that a large amount of crystal defects having a density of 10.sup.8 /cm.sup.2 -10.sup.11 /cm.sup.2 will occur in the crystals grown on the C surface sapphire or Si substrate. As a result, it is impossible to obtain a crystal film having a good quality and an excellent crystallinity.
Accordingly, it has been suggested that ZnO film be formed as a buffer film on the C surface sapphire substrate and Si substrate. Although it is possible to obtain a good quality ZnO orientated film with the light emitting element obtained by forming an In.sub.x Ga.sub.y Al.sub.z N layer on the C surface sapphire substrate through ZnO film, there is a problem in that such a substrate has to be manufactured with a high cost. Further, with the light emitting element obtained by forming a In.sub.x Ga.sub.y Al.sub.z N layer on the Si substrate through the ZnO film, although such a substrate can be manufactured with a low cost, there is another problem in that it is impossible to obtain a ZnO orientated film with a good quality, whereby it is further impossible to grow a In.sub.x Ga.sub.y Al.sub.z N having an excellent crystallinity on the ZnO film.